I had the idea of making the fixture as a molded plastic part, should be an easy (and cheap) mold to make, and supply one with each base. This would allow you to eliminate the "fingers" on the base - I'm assuming that the molds to include the fingers were expensive, plus I'm sure that there are a percentage of parts where the fingers get damaged or broken off in shipping and handling. The separate gauge would be a simple solution. Plus, your customer would have an easy way of switching the base to another saw while still keeping the required 3" distance.